Common examples of electrical devices include wire and cable applications. Typical power cables include one or more electrical conductors in a core that is surrounded by several layers that can include a polymeric semiconducting shield layer, a polymeric insulating layer and another polymeric semiconducting shield layer, a metallic tape, and a polymeric jacket. Thus, a wide variety of polymeric materials have been used as electrical insulating and semiconducting shield materials for wire, cable, and numerous other electrical applications.
Polymerized elastomer or elastomer-like polymers are often used in power cables. Ethylene, C3–C12 α-olefin, and C5–C20 non-conjugated diene monomers form these elastic materials. Polymers containing ethylene, either homopolymers or copolymers with C3–C20, olefinically unsaturated comonomers, are also used as insulating layers or semiconducting layers. See for example, U.S. Pat. Nos. 5,246,783, 5,763,533, International Publication WO 93/04486, and generally, “Electric Insulation”, Kirk-Othmer Encyclopedia of Chemical Technology, 4th Ed., pages 627–647 (John Wiley & Sons, 1993). Dielectric strength, electrical resistivity, electrical conductivity, and dielectric constant are all important characteristics for these applications.
Polymerization of olefinically unsaturated monomers is well known and has led to the proliferation of elastomeric and plastic materials, such as polyethylene, polypropylene, and ethylene-propylene rubber. Catalyst compounds with bulky, stabilizing-ligand-containing metal cation components are now well known in the art. Examples include cyclopentadienyl-ligand-containing transition metal compounds (e.g., metallocenes), bisamido- and bisimido-ligand-containing transition metal compounds, as well as other metal compounds that are stabilized by incorporating bulky ligands. Cocatalyst compounds containing, or capable of providing, non-coordinating anions can be used to stabilize the transition metal cations and maintain their cationic form rendering them suitable for olefin oligomerization and polymerization, see for example U.S. Pat. No. 5,198,401. This and related references describe metallocene compound protonation by anion precursors to form stable catalysts.
U.S. Pat. Nos. 5,427,991, and 5,643,847 specifically teach the use of anionic complexes directly bound to supports through chemical linkages to improve polymerization processes that are conducted under slurry or gas-phase polymerization conditions. See also U.S. Pat. No. 5,939,347 which addresses protonating or abstracting cocatalyst activators bound to silica.
Low crystallinity ethylene-containing elastomers and ethylene-containing polymers can be produced under gas-phase or slurry conditions, but are more typically prepared by solution polymerization processes, in part because these polymers have good solubility in commonly used hydrocarbyl solvents see the supported-catalyst references cited above. Examples include: U.S. Pat. No. 5,198,401 (above), U.S. Pat. Nos. 5,278,272, 5,408,017, 5,696,213, 5,767,208 and 5,837,787; and, EP 0 612 678, EP 0 612 679, International Applications WO 99/45040 and WO 99/45041. Although each reference, in part, addresses ethylene-containing polymers prepared with ionic catalyst compounds; preparing satisfactory electrical device polymers from these solution processes has unsolved problems. Using noncoordinating or weakly coordinating anion cocatalyst complexes poses a problem because it leaves labile, anionic-charge-carrying species as a byproduct within the resulting polymeric resins or matrices. These mobile anions adversely affect both dielectric strength and dielectric constant.
Additionally, olefin solution polymerization processes are generally conducted in aliphatic solvents that serve both to maintain reaction temperatures and solvate the polymer products. But aryl-group-containing catalysts, those having cyclopentadienyl derivatives and other fused or pendant aryl-group substituents, are sparingly soluble in such solvents and typically are introduced in the aryl solvents such as toluene. Because of health concerns, the aryl solvent must be removed. Also, aryl solvents reduce process efficiencies making their presence undesirable. Alternatively, relatively insoluble catalysts can be introduced using slurry methods, but such methods required specialized handling and pumping procedures that complicate industrial scale plant design and add significant costs to plant operation. Typical slurry compositions cause significant wear on pumps, piping, joints, and connectors. Low solubility also poses a problem when the processes involve low temperature operation at some stage such as typically seen in adiabatic processes run in colder climates. The adiabatic reactor is operated at ambient temperature. Thus, the catalyst's low solubility is further lowered by a colder reaction temperature. Additionally, counteracting the build-up of aryl solvents in the recycle system, or separating them from the system, presents added problems. At the same time, maintaining high molecular weights in olefin polymers while operating at economically preferable high reaction temperatures and high production rates is highly desirable.